2012 Toyota Prius Plug-In: By The Numbers, Would It Work For You?

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Over six days of driving—limited to around-town trips—we put about 103 miles on a fleet-test Toyota Prius Plug-In, averaging 90.8 miles per gallon. In that time, we gave the Prius Plug-In five full charges and two partial ones, and according to the trip computer, we covered 77.7 miles in EV mode.

As we've reported in prior driving impressions, the Plug-In, which won't go on sale until spring of 2012, will move on—or primarily on—electric power for up to 14 or so miles per charge, and a full charge only takes about three hours with a standard 110V household power outlet.

There are several conversation points here, and it takes some juggling of figures to get a grasp of whether the plug-in might be right for you. That starts with two big questions: Firstly, how much does the Prius cost to run on electric power versus normal hybrid operation; and secondly, what's the net difference in carbon footprint and emissions?

Both of those answers are going to be dramatically different from family to family, depending on how often you remember to plug in, how far you travel per trip and each day, and whether it's possible or convenient at waypoints.

Charges cost less than 50 cents a pop

First, the cost-of-ownership question. According to Toyota spokesman John Hanson, the Prius PHEV only uses about 3.8 kWh of the battery's 5.2-kWh capacity (for battery longevity). Starting with what electricity costs me here in Portland, Oregon—11.7 cents per kWh, slightly higher than the 11.04-cent national average at the end of last year—that pegs each full charge at about 44 cents. With a total of about six charges, given the five full charges and two partial ones, that puts our total cost of electricity at about $2.67.

In a driving style that's comparable to what we followed with the Plug-In—which is to say gentle and careful, with only a couple of exceptions to test the power on tap—we've seen in the range of 48 mpg in the standard Toyota Prius. So we would have used about 2.15 gallons of gasoline in a non-Plug-In model. At the current national average of about $3.54 a gallon, that's $7.61 in a standard Prius to cover those 103 miles. In our PHEV test car, we used 1.13 gallons ($4.01), plus that $2.67 in electricity—bringing our total for the PHEV of $6.68.

Just to index this in some way, here it is adjusted for 100 miles, at the average cost of residential electricity:

Prius Plug-In (100 miles): $6.12
Standard Prius (estimate, 100 mi): $6.98
Difference per 100 miles: $0.86
Difference per 10,000 miles: $86
Difference per 100,000 miles: $860

Payback? Probably not.

With the 2012 Toyota Prius Plug-In expected to sell at $3,500 to $5,000 more than a comparable Prius, payback in this traditional sense probably isn't going to happen—even if gas prices double.

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Comments (15)
  1. Nice discussion. Glad some authors on Green Car Reports consider both emissions and cost.
    One small point. You drove 103 miles and did 6 full charges. Each charge should give 14 miles for a total of 84 miles electric. The you burned 1.13 gallons of gas at 48 mpg. That should be 54 miles for a total of 84+54=138 miles not 103 miles. That is a 34% error.
    It would really have been better to use a power meter to see how much energy comes out of the wall plug.

  2. Regarding the economics: The Prius is damned by its own success. Always hard to get additional savings when you are not spending much to begin with.
    Also, one point not discussed is the relative economics of the plug-in Prius versus the Chevy Volt. Presumably the Prius is much cheaper (although there is the rebate issue) but much less of a range. Is the most appropriate range 14 miles or 40 miles?

  3. Hi John,
    Those calculations were based on the trip computer's assessment that I drove 77.7 miles in EV Mode. But I know the numbers don't work out then either (a precise tally of kW used and gallons used would be a must in my opinion, a feature the vehicle itself doesn't have now). My first guess as to why this would be is that what's considered HEV mode is probably less efficient when it's mostly kicking in for extra power of accessory demands. We're eager to see some of the data from fleet studies and will of course cover this again when it's released.

  4. I don't wish to sound too much like a broken record but the emissions from the gasoline used should be included, not just what comes out of the tailpipe but what went in to making it. 2.49Lbs / gallon from this paper http://www.scribd.com/doc/31294978/CO2-Emissions-From-Refining-Gasoline

  5. many people could easily get by on 20km or 14miles of driving per day and could charge up car from solar panels on house. really then they would have almost no gas to buy and no emissions. usa sends its wealth to middle east for oil but electricty from wind and solar keep money in the country much more.

  6. @Michael-- Agreed and thanks; the carbon cost of refining isn't trivial. Using that estimate we'd have ~ another quarter-ton of emissions a year for the regular Prius (less of course for the plug-in, and a smaller difference).

  7. @Bengt Halvorson,
    Think you meant to say KWH not KW. We have a long way to go in our common understanding of EVs.

  8. Thanks Bengt, we need more fact-data driven writers like you around here...I think all the controversy about cars' gas mileages rests on two facts: 1. The reports that come from the manufacturer are based on ideal lab conditions, which sets a standard of little to no use about how many mpg a car can or cannot do 2. As you stated, gas mileage strongly depends on driving style...But $6.68 per 100 miles make a lot of sense to me. With my driving style, I expend $8.50-$10.00/day to cover about 60 miles with a car that returns 30mpg when driven @ about 50mph average...I will definitely buy a Plug in Prius...

  9. Bengt,
    You forgot to mention about the $2,917 tax credit and the HOV lane access with a single driver.
    At 22kWh/100 miles electricity consumption, Prius PHV is the most efficient plugin.
    How can the longer range plugins like Leaf (34kWh/100 miles) or Volt (36kWh/100 miles) that consume more electricity per mile make more economical sense?

  10. @Dennis - They make more sense if you drive more and want to cut gasoline purchases and emissions down to nothing (LEAF much more than Volt obviously.) For me it would be LEAF, then plug-in Prius, lots of other options, and then Volt at the bottom of the list since it costs so much and I'd have to leave my baby behind :-)

  11. Even using Nissan technology which is pretty poor in terms of energy density (about 80WH/KG at the pack level) the 5.2 KWH plug-in Prius battery shouldn't weigh more than 150 pounds. So I wonder where the 300 pounds of EXTRA weight comes from.

  12. Michael, you bring up the essential point that we need to consider full life-cycle carbon dioxide emissions for the gasoline, well-to-wheels. The same is true for the energy used to produce the electricity, of course, which varies depending on location. In the case of coal, that'd be mine-to-wheels. How do you apportion the CO2 emissions from building and maintaining a dam to provide hydroelectric power over decades? To my mind, it makes no sense to compare CO2 emissions from a regular Prius to a Plug-in Prius using the average CO2 emissions for the national grid. Unfortunately, these questions have to be addressed by each individual based on the energy mix used by her/his utility provider.

  13. There is one point I have not seen mentioned above. Recently while park at work, I saw my first car plugged into the wall. It was a Volt. I checked the area and there were about 6 plugs in that corner of the garage. For the plug-in Prius, getting some free kWh every work day improves the economics immensely versus the standard Prius. Of course the same improvement applies to the Volt. If you can keep the Volt in pure electric it can beat out the Prius, but the Volt's gas engine "only" gets around 38 MPG.

    Anyway, get to work at 8:30-9, plug-in. Go to lunch at noon fully charged. Plug-in again and you are fully charged for the trip home. You may be getting 1.5 - 2 free charges per day (0.66-0.88). My commute is 18 miles.

  14. I have not been looking for it, but I would not be surprised if shopping malls or businesses targeting "green" consumers (Whole Foods?) have at least some basic (110V plug) charging stations. If they don't already, maybe they will when there are enough plug-ins on the roads?

  15. I just bought a Prius plug-in for 32,000. I am interested in the conversation, and my experience is too limited at this point to make any comparisons. The only thing I can say is driving around town on short trips with out using any fuel is great. Also, as a hybrid, it will not leave you stranded, if you drive it for a long distance. Charging stations are being built, but still not adequate. I am still collecting data or cost of driving and carbon footprint. So far, I like the car.

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